fix KT-7042 Providing return type for property setter is not reported as error

#KT-7042 Fixed

compiler/testData/diagnostics/tests/backingField/SetterWithExplicitType.kt

@@ -0,0 +1,26 @@
+// KT-7042 Providing return type for property setter is not reported as error
+
+var x: Int = 1
+
+// No backing field!
+var y: Int
+    get() = x
+    set(value): <!WRONG_SETTER_RETURN_TYPE!>Any<!> {
+        x = value
+    }
+
+var z: Int
+    get() = x
+    set(value): Unit {
+        x = value
+    }
+
+var u: String = ""
+    set(value): Unit {
+        field = value
+    }
+
+var v: String = ""
+    set(value): <!WRONG_SETTER_RETURN_TYPE!>String<!> {
+        field = value
+    }

compiler/testData/diagnostics/tests/backingField/SetterWithExplicitType.txt

@@ -0,0 +1,7 @@
+package
+
+public var u: kotlin.String
+public var v: kotlin.String
+public var x: kotlin.Int
+public var y: kotlin.Int
+public var z: kotlin.Int